Body in white structures often require one-sided joining techniques in order to create design efficient assemblies. One such technique is flow drill screwing (FDS) where a threaded fastener is screwed to a sheet-metal and/or extrusion joint and the “nut” is created in situ during the insertion process. When installing a flow drill screw S in thick gauge material stack ups or when the top layer of sheet material is greater than a governing size (e.g. greater than 3 mm), a clearance hole has been used in the past in the top sheet of material. This has been done because an upward flow of metal during screw insertion often forces a gap G between the layers L1, L2 of the joint (see FIG. 1). This gap G is mitigated with the presence of the clearance hole.
While a clearance hole will effectively solve the gapping problem, a clearance hole is undesirable because it (1) potentially weakens the joint, (2) introduces a stress concentration and (3) often requires a vision system during body assembly to ensure that the flow drill screw is inserted properly into the clearance hole.
United States Patent Application Publication No. 2013/0195579, assigned to Ford Global Technologies, LLC, discloses one possible approach for eliminating the need for the clearance hole. In accordance with the teachings of this document, an indentation or a void is provided in one of the workpieces to be joined with that indentation facing inwardly toward the other workpiece to be joined. The flow screw is then inserted through the indentation with the material being displaced into the indentation. While this approach is useful in that it eliminates the need for a clearance hole when fastening workpieces with a flow drill screw, it should be appreciated that an indentation formed in one workpiece facing toward the other workpiece that are being joined together cannot be readily detected visually or otherwise. Accordingly, the approach disclosed in the '579 document is not convenient and does not always allow the most efficient assembly in many situations.
This document relates to a new and improved flow drill screw assembly and method wherein one of the workpieces includes an exposed groove that may be more easily detected visually or by other means to ensure that the flow drill screw is properly positioned in order to complete the assembly.